Thomas Ravens

Thomas Ravens
University of Alaska Anchorage | UAA · College of Engineering

Ph.D.

About

37
Publications
4,218
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Introduction
Tom Ravens currently works in the College of Engineering, at the University of Alaska Anchorage. Tom does research in Arctic coastal processes as well as hydrokinetic energy.

Publications

Publications (37)
Article
Full-text available
The significant increase in the Arctic open-water extent along with the earlier sea-ice summer melt and later autumn freeze-up seasons observed in the last decades allow the formation of less fetch-limited waves and the further propagation of storm surges to new ice-free shores. Coupled hydrodynamic and wave models can be used to simulate these com...
Article
Full-text available
Two prominent arctic coastal erosion mechanisms affect the coastal bluffs along the North Slope of Alaska. These include the niche erosion/block collapse mechanism and the bluff face thaw/slump mechanism. The niche erosion/block collapse erosion mechanism is dominant where there are few coarse sediments in the coastal bluffs, the elevation of the b...
Preprint
Full-text available
In the Arctic, air temperatures are warming and sea ice is declining, resulting in larger waves and a longer open water season, all of which intensify the thaw and erosion of ice-rich coasts. This change in climate has been shown to increase the rate of Arctic coastal erosion, causing problems for industrial, military, and civil infrastructure as w...
Conference Paper
Full-text available
In the event of an Arctic oil spill, ice in the water is a complicating factor. The presence of ice complicates the forecasting of the movement and spreading of oil as well as the planning of the oil spill clean-up process. The underside of Arctic Sea ice is not flat, rather it presents non-geometric, unpredictable protrusions into the water column...
Article
Full-text available
During two field seasons, a 1.93 m diameter, open-center style, hydrokinetic device was deployed from a pontoon barge in the Tanana River, in Alaska. Near-surface velocity was roughly 1.7 m/s and 2 m/s at the deployment site during September 2014 and July 2015, respectively. Velocity and turbulence were measured in the vicinity of the turbine locat...
Chapter
An Arctic coastal erosion process or mechanism is distinct from a non-Arctic erosion process due to the importance of thermal processes in addition to mechanical ones. The Arctic contains permanently frozen soil (permafrost) as well as soil and sediments that freeze seasonally. Thawing of the coastal permafrost and seasonally frozen soils/sediments...
Article
Full-text available
Increased maritime activities and rapid environmental change pose significant hazards, both natural and technological, to Arctic maritime operators and coastal communities. Hazard assessment and emergency response are hampered by a lack of dedicated hazard monitoring installations in the Arctic. Currently, U.S. and foreign research activities accou...
Article
Full-text available
Arctic coastal morphology is governed by multiple factors, many of which are affected by climatological changes. As the season length for shorefast ice decreases and temperatures warm permafrost soils, coastlines are more susceptible to erosion from storm waves. Such coastal erosion is a concern, since the majority of the population centers and inf...
Article
The work discussed here is a continuation of the study presented in [1], in which a customized test apparatus was presented that was capable of conducting tribological related experiments on sliding components commonly used in hydrokinetic devices such as bearings, drive shaft and seals. The wear on critical sliding components introduces unnecessar...
Article
Non-cohesive soils are extensively distributed in Interior Alaska and soil erosion in a newly constructed roadside embankment is of great concern. Geofibers and nontraditional additives have been used for stabilizing non-cohesive soils and controlling soil erosion. However, in cold regions where permafrost exists such as Interior Alaska, any erosio...
Article
Hydrokinetic devices have lately reemerged as a promising solution for harnessing energy from renewable sources such as rivers, tidal currents, or artificial channels. This paper describes a customized test flume that is capable of conducting tribological related experiments on sliding components (bearing, shaft, and generator seals) commonly used...
Article
Full-text available
A simple technique to estimate the far-field hydraulic impacts associated with the deployment of hydrokinetic devices is introduced. The technique involves representing hydrokinetic devices with an enhanced Manning (bottom) roughness coefficient. The enhanced Manning roughness is found to be a function of the Manning roughness, slope, and water dep...
Book
Full-text available
More than 50 percent of Americans live in coastal watershed counties, a percentage that continues to increase (see section 1.3). In addition, the coast is home to the majority of major urban centers as well as major infrastructure such as seaports, airports, transportation routes, oil import and refining facilities, power plants, and military facil...
Article
Full-text available
A process-based coastal erosion/shoreline change model has been developed for Arctic coastal bluffs subject to niche erosion/block collapse. The model explicitly accounts for many environmental/geographic variables including: water temperature, water level, wave height, and bluff height. The model was originally developed for a small coastal segmen...
Conference Paper
The emergence of hydrokinetic energy generating technologies presents new opportunities to generate electricity from the nation’s rivers and streams. The nature and magnitude of any impacts on fishery resources will depend in part on the locations in which hydrokinetic technologies are deployed, the density with which the devices are deployed, and...
Article
Full-text available
A predictive coastal erosion/shoreline change model has been developed for the North Slope (Alaska) coast by Drew Point. This coastal area has been experiencing rapid and accelerating erosion in the past few decades (to about 20 m/yr in the recent past). The coast has 3-m high permafrost bluffs with high ice content and fine-grained soils. The bluf...
Article
This study challenges the paradigm that salt marsh plants prevent lateral wave-induced erosion along wetland edges by binding soil with live roots and clarifies the role of vegetation in protecting the coast. In both laboratory flume studies and controlled field experiments, we show that common salt marsh plants do not significantly mitigate the to...
Article
There is major salt marsh loss in Galveston Bay and other estuarine environments. In Galveston Bay, the causes of marsh loss include wave action, subsidence, eustatic sea-level rise, and insufficient sediment supply. To assess the relative importance of these factors in marshes of West Galveston Bay, wave action, sediment supply, and sedimentation...
Article
This paper analyzes the effect of flume test section length on sediment erodibility measurements. A modular flume was constructed and experiments were conducted with two test section lengths: 0.15 and 1.10 m. The internal height and width of the flume were 0.11 and 0.13 m, respectively. A fine (7 mu m) commercially available quartz sediment was use...
Article
Longshore sediment transport in the surf zone on Galveston Island, Texas, was studied to develop a new technique involving optical instruments rapidly calibrated in situ and to compare measured transport rates with those predicted by the well-known Coastal Engineering Research Center (CERC) formula. This method used an instrumented sled equipped wi...
Article
Full-text available
During the summer of 2005, a tidal creek ("Pine Gully") within a few km of the Houston Ship Channel was completely blocked by a 200-m long and 1.5-m deep plug of silt and fine sand. This paper documents and explains this unusual sedimentation event. It then presents a new method for calculating ship wave-induced sediment transport into tidal creeks...
Article
In 1955, Narwhal island was a 4 km long and 30 to 200 m wide barrier island, located at 145 30' W; 70 24' N, about 20 km offshore of the North Slope coast by Foggy Island Bay and near Prudhoe Bay, Alaska. According to available aerial photography, by 1979, the island had been breached in 4 locations creating a five island chain. By 1984, the chain...
Article
This paper compares the results of two sediment erodibility test methods that have been applied on surficial sediments at a number of locations on the Fox River in Wisconsin. The methods include a straight flume that is deployed in situ (the FLUME) and a straight laboratory flume (the SEDFLUME). The sediment erosion rates measured near the surface...
Article
Computational fluid dynamics calculations of flow in a straight flume for sediment erodibility testing were conducted. The calculations allowed improved postprocessing of the erosion data collected and better understanding of scour pit formation that is sometimes found in the flume's test section. The flume is a 3-m-long, rectangular (13-cm-wide by...
Conference Paper
Full-text available
During the summer of 2005, a tidal creek (\“Pine Gully”) within a few km of the Houston Ship Channel (USA) was totally plugged up with a 200-m long and 1.5-m deep plug of silt and fine sand. The volume of the plug was about 1,800 cubic meters. The seaward end of the plug was about 200 m landward of the creek’s inlet. Between November 2005 and Janua...
Article
were analyzed with a sediment budget to infer the longshore and cross-shore (out of the littoral system) transport. The analysis indicated a relatively calm period from 1990 to 2001, which was dominated by longshore transport, as well as two hurricane-prone periods (1956–65 and 1965–90), which had both longshore and cross-shore transport. The Wave...
Article
Full-text available
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1997. Includes bibliographical references (p. 182-183). by Thomas M. Ravens. Ph.D.
Article
Longshore sediment transport in the surf zone on Galveston Island, Texas, was studied using a instrumented sled that was pulled across the surf zone. Determination of the sand transport rate was challenging due to presence of fines. The instrument sled contained a LISST 100 for particle size distribution determination, four OBS sensors, and three v...
Conference Paper
A project is currently underway to create marshes in Galveston Bay using dredged materials. Two hundred acre earthen boxes (cells) were built in various locations in the bay and dredged materials were pumped in. In this paper we report on our efforts to design tidal creeks for two adjacent cells, north of Bolivar Peninsula. The creeks will be cut o...
Article
We studied cold, deep-water intrusions in the South Basin of Lake Baikal on the basis of 2 yr of data (December 1995–November 1997) from near-bottom and near-surface thermistor strings, monthly conductivity–temperature– depth (CTD) profiles, and a near-bottom current meter, all collected near the South Basin maximum depth of 1,461 m. The data show...
Article
Full-text available
The water column of Lake Baikal is extremely weakly—but permanently—stratified below 250 m. Despite the thickness of this relatively stagnant water mass of more than 1000 m, the water age (time since last contact with the atmosphere) is only slightly more than a decade, indicating large-scale advective exchange. In the stratified deep water, the fa...
Article
To obtain in situ measurements of sediment erodibility in defined bottom shear stress environments, a portable, straight flume was built, tested, and deployed in the field for six experiments at three locations in Quincy Bay of Boston Harbor, Mass. The flume had a 1.0-m-long inlet section, which included a boundary-layer trip and a roughened, plexi...
Article
Full-text available
Calculated annual excess skin friction stress at various locations in Quincy Bay (outer Boston Harbor) was found to be correlated positively with sediment sand content. The correlation was optimized when a critical shear stress (τc) of 0.085 Pa was assumed for the bay. The excess shear stress was correlated negatively with sediment lead (Pb) and po...
Article
This paper explores the concept of continuously extruding reacting polyurethane foams. The control of the process is hampered by the fact that the state of the conversion of the extrudate is not directly observable. We present the general concept, describe an experimental apparatus, present a mathematical model of the process, and report on some in...

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